The four hymns are from the Guru Granth Sahib, the Sikh holy scriptures and appear on Ang 773 to 774 of the total of 1430.
The Guru tells of the four spiritual stages of married life and how the couple as a team have to first begin by following the path of righteousness and sinless-ness.
The main part of the Anand Karaj (Sikh Marriage Ceremony) is the reading and then the singing of each laav.
While the laav is sung, the couple, joined by a piece of cloth, circle the Guru Granth Sahib.
The Sri Guru Granth Sahib is the spiritual center and the Sadh Sangat is the worldly (temporal) witness and support.